This type of technique is conventionally known as disclosed for example in Patent documents 1 to 4 listed below. In particular, in an engine provided with a supercharger in an intake passage, a blowby gas returning apparatus disclosed in Patent document 1 includes a fresh-air introduction passage to introduce fresh air from the intake passage into a head cover, a first blowby gas returning passage to return the blowby gas accumulated in a crank case to the engine during operation of the supercharger, and a second blowby gas returning apparatus to return the blowby gas accumulated in the head cover to the engine during non-operation of the supercharger. An inlet of the first blowby gas returning passage and an inlet of the second blowby gas returning passage are connected individually to blowby-gas accumulation parts (the crank case, the head cover).
In the apparatus disclosed in Patent document 1, since the inlet of the first blowby gas returning passage and the inlet of the second blowby gas returning passage are connected to the different accumulation parts (the crank case, the head cover) placed apart from each other, any problem with backflow of gas between the inlets does not occur.